1. Field
The disclosure relates generally to the field of diagnostics and detection. More particularly, the disclosure relates to low resource processors for assessing molecular interactions. Specifically, the disclosure relates to a variety of lateral flow assays that employ beads with capture agents, and they processing and delivery to a chromatographic substrate. In a particular aspect, the beads are magnetic, and may employ “catch and release” chemistries. Specific devices containing multiple chambers that are in fluid connection and that facilitate the delivery of samples to commercial rapid diagnostic test cassettes that are inserted into the device. The device permits assaying for the content of a wide variety of environmental and biological samples, including whole cells.
2. Description of Related Art
The advent of point of care (POC) diagnostic tools has changed the face of healthcare in nations affected by the ongoing spread of infectious diseases (Yager et al., 2008). These underdeveloped, remote areas are often characterized by poverty, absent or intermittent electricity, hot and humid environmental conditions as well as a lack of skilled clinicians. Lateral flow immunochromatographic rapid diagnostic tests (RDTs), which operate much like a commercial pregnancy test, were developed to circumvent these challenges and bring affordable disease diagnosis to low resource areas (Murray and Bennett, 2009; Murray et al., 2008). Several advantages of RDTs include low cost, rapid time to result, and ease of use and interpretability (Bell and Peeling, 2006).
Additionally, these tests have been widely used in public health programs to aid with patient management, disease surveillance and treatment campaigns (D. Bell and M. Perkins, 2012). In 2006, over 16 million RDTs were delivered to underdeveloped nations for the detection of malaria alone (C. K. Murray and J. W. Bennett, 2009). These RDTs detect protein biomarkers of the malarial parasite. The predominant RDT biomarker indicative of Plasmodium falciparum infection is Histidine Rich Protein II (pfHRPII), while Plasmodium Lactate Dehydrogenase (pLDH) serves as a pan-specific biomarker (Murray and Bennett, 2009).
Despite the many advantages of RDTs, the changing climate of infectious disease education, prevention, and treatment has highlighted the need for improved tests. The World Health Organization (WHO) periodically reviews all malaria RDTs manufactured for diagnostic use, and sets the limit of detection for these tests at 200 parasites/μL (World Health Organization, 2011). While this limit of detection is sufficient for the diagnosis of symptomatic malaria infection many asymptomatic patients are not diagnosed and continue to be transmission reservoirs of the disease because current RDTs fail to identify these asymptomatic carriers. Additionally, poor manufacturing standards and storage conditions render many brands of malaria RDTs inoperable and unreliable (Wongsrichanalai et al., 2007). There are an estimated 60 brands and 200 types of tests manufactured for the detection of malaria, and according to the WHO, less than 10% of those tests are effective at detecting 200 parasites/μL parasite densities (Malaria Rapid Diagnostic Test Performance Results, WHO 2011. Unfortunately, tests are often acquired based on government sanctions, history of use, and cost instead of acquisition based on reliability of the brand (Bell et al., 2006). This variability in test performance, sensitivity and reliability undermines the progress made in malaria disease prevention (Gubala et al., 2011).
The inventors have recently reported the development of a low resource extraction cassette that can extract, purify and concentrate the most common malarial biomarker, Plasmodium falciparum Histidine Rich Protein II (pfHRPII), from a blood sample, in less than 30 minutes (Davis et al., 2012). In this study, a series of aqueous buffer solutions separated by air and oil surface tension valves were preloaded into a single length of tubing. They were able to purify the protein biomarker from blood by processing biomarker bound magnetic particles through the cassette using a handheld magnet. At least 50% extraction efficiency was demonstrated for samples with parasitemias as low as 12.5 parasites/μL and, as a result of this technique, a commercial RDT brand was qualitatively improved over 8-fold. Nonetheless, it would be useful to have a simpler design that would provide for high quality samples useful in commercial RDT devices in low resource environments.
However, even RDTs are limited to a certain extent by the nature and quality of samples being tested. For example, RDTs, including lateral flow assays (LFAs) produce more signal if more biomarkers are added, and thus are better able to detect biomarkers. Adding more patient sample to an LFA is one way to add more biomarkers; however, LFAs will not function with patient sample volumes greater than 20-40 μL (depending on the LFA size and material composition) because (i) LFA test strips have a limited capacity, and (ii) larger volumes of patient samples contain more cellular debris, which inhibit the capillarity the drives the assay. Therefore, additional solutions for these problems also would be of significant value.